A vehicle equipped with an automatic engine stop/start control system (an idle reduction control system) has been developed in order to improve fuel economy and reduce emission. In a conventional automatic engine stop/start control system, when a driver stops a vehicle, a fuel injection is stopped to stop the engine (fuel cut) automatically. Then, when the driver operates to start the vehicle, a starter automatically cranks the engine to restart.
However, it is insufficient to improve fuel economy by performing the fuel cut only when the vehicle is stopped. JP-2002-274224A (U.S. Pat. No. 6,702,718) and JP-8-189395A show that a fuel cut is performed to stop the engine also when the vehicle is decelerated and the vehicle may be stopped.
In the idle reduction control system shown in JP-2002-274224A, when the vehicle is decelerated and the engine is automatically stopped, a gear of the transmission mechanism is changed to a specific gear having a one-way clutch to interrupt a transmission of a driving power from the driving shaft to the engine. The engine is stopped rapidly to pass through a resonant vibration region of the vehicle so that a vehicle vibration is reduced.
However, when the engine is rapidly stopped, an intake air pressure which is a negative-pressure source of a brake is rapidly increased to atmospheric pressure. Thus, if the engine is rapidly stopped in a deceleration condition of the vehicle by the idle reduction control, a brake performance may be deteriorated. Besides, in a vehicle equipped with the idle reduction control system, an electric hydraulic pump driven by a battery is used as a hydraulic pump for driving engine in order to ensure the hydraulic pressure of the automatic transmission during an engine stop period by the idle reduction control. When the engine is rapidly stopped by the idle reduction control before the vehicle is stopped, a driving period of the electric hydraulic pump is prolonged and an electric power consumption of the electric hydraulic pump (battery discharge) is increased. In view of ensuring an amount of charge of the battery, a battery-charge control system restricts the idle reduction period, so that an improvement of fuel economy is deteriorated.
JP-8-189395A shows a vehicle equipped with a transmission including a clutch of which torque clutch capacity is electrically adjustable. In this vehicle, while the fuel cut is performed to automatically stop the engine of the vehicle which is decelerated, a clutch is engaged until a specified clutch disengage condition is satisfied, so that an effective region of the engine brake is enlarged. When the specified clutch disengage condition is satisfied, the clutch is disengaged to interrupt the driving power transmission from the driving shaft to the engine, so that a vehicle vibration is reduced at the engine stop.
However, in the above configuration, since the clutch is engaged between the driving shaft and the engine until the clutch disengage condition is satisfied, it is likely that a large shock is directly transmitted from the driving shaft to the engine if a disengaging timing of the clutch is delayed even slightly. In contrast, if the clutch is disengaged early, the effective region of the engine brake is decreased.